The goals of the proposed work are: 1) to examine the role of cholera-like, heat-labile toxin of E. coli in sporadic infintile diarrhea and 2) to examine the relationship between the acquisition of toxigenic fecal bacteria and development of the immune response to toxin. Work is proceeding to achieve these goals by weekly sampling of a cohort of normal babies to compare episodes of diarrhea with acquisitio of toxigenic bacteria. Sera from birth to two years of age (q. six-monthly and acute and convalescent samples surrounding individual episodes of diarrhea) are available for determination of toxin-specific immunoglobulins at the conclusion of the study.